In-liquid Plasma Research Articles

In-Liquid Plasma Recycling Method of Zinc Oxide Nanoparticles

In-Liquid Plasma Recycling Method of Zinc Oxide Nanoparticles

Synthesis of Silicon and Silicon Carbide Nanoparticles by Pulsed Electrical Discharges in Dielectric Liquids

Silicon carbide (SiC) has been widely used in many applications, which require high mechanical endurance or high electrical resistance. It also serves as a basic material for light emitting diodes. Here, we present an in-liquid plasma method to produce SiC nanoparticles. A sustained spark-discharge in a dielectric liquid, which is energized by a nanosecond pulsed power supply, is established for the synthesis. To provide Si and C, we employed graphite and silicon as electrodes and cyclohexane (CHX) and tetramethylsilane (TMS) as dielectric liquids. For a reasonable comparison, we tested various combinations of electrode and liquid, namely Si-to-C in CHX, Si-to-Si in CHX, and C-to-C in TMS. We found that discharges in CHX produce Si particles encapsulated in C-shell and Si nanoparticles in C-matrix. Meanwhile, discharges in TMS consistently produce SiC nanoparticles with an average size of ~ 10 nm, regardless of the electrode material.

Novel synthesis of nickel ferrite magnetic nanoparticles by an in‐liquid plasma

Magnetic nanoparticles of nickel ferrites were successfully synthesized by the in-liquid plasma method. The synthesis process is performed in three different solutions. The anode material is made of iron and nickel powder by Spark Plasma Sintering (SPS) process. By discharging on the anode’s surface in the solution, a plasma forms on the electrode surface, and nanosize particles detached from the electrode and immediately oxidized into a ferrite spinel. Spectroscopic, morphological, structural, and magnetic characterization showed that the electrolyte type significantly affects nanoparticle features. The X-ray diffraction of nanoparticles confirms the formation of spinel NiFe2O4, and the highest crystallinity has belonged to the nanoparticles synthesized with ethanol and sodium hydroxide. Based on the results, the particles synthesized in the optimum solution are spherical with an average size of ~ 10 nm, and their specific surface area is significantly enhanced to 55.237 m2/g. A ferromagnetic property with 89.75 Oe coercivity and a saturation magnetization of 42.27 emu/g has been measured for the synthesized powders at room temperature.

Plasma-Assisted Synthesis of Multicomponent Nanoparticles Containing Carbon, Tungsten Carbide and Silver as Multifunctional Filler for Polylactic Acid Composite Films.

Multicomponent nanoparticles containing carbon, tungsten carbide and silver (carbon-WC-Ag nanoparticles) were simply synthesized via in-liquid electrical discharge plasma, the so-called solution plasma process, by using tungsten electrodes immersed in palm oil containing droplets of AgNO3 solution as carbon and silver precursors, respectively. The atomic ratio of carbon:W:Ag in carbon-WC-Ag nanoparticles was 20:1:3. FE-SEM images revealed that the synthesized carbon-WC-Ag nanoparticles with particle sizes in the range of 20–400 nm had a spherical shape with a bumpy surface. TEM images of carbon-WC-Ag nanoparticles showed that tungsten carbide nanoparticles (WCNPs) and silver nanoparticles (AgNPs) with average particle sizes of 3.46 nm and 72.74 nm, respectively, were dispersed in amorphous carbon. The carbon-WC-Ag nanoparticles were used as multifunctional fillers for the preparation of polylactic acid (PLA) composite films, i.e., PLA/carbon-WC-Ag, by solution casting. Interestingly, the coexistence of WCNPs and AgNPs in carbon-WC-Ag nanoparticles provided a benefit for the co-nucleation ability of WCNPs and AgNPs, resulting in enhanced crystallization of PLA, as evidenced by the reduction in the cold crystallization temperature of PLA. At the low content of 1.23 wt% carbon-WC-Ag nanoparticles, the Young’s modulus and tensile strength of PLA/carbon-WC-Ag composite films were increased to 25.12% and 46.08%, respectively. Moreover, the PLA/carbon-WC-Ag composite films possessed antibacterial activities.

Deposition of carbon–tungsten carbide on coir pulp to improve its compatibility with polylactic acid

To increase hydrophobicity of surfaces of coir pulp, carbon–tungsten carbide (WC) was synthesized and simultaneously deposited on coir pulp by applying in-liquid electrical discharge plasma, so-called solution plasma process (SPP). As a result, water contact angle of carbon-WC deposited coir pulp was 123.4°, whereas that of coir pulp was 82.8°. The carbon-WC deposited coir pulp was then used as a filler in polylactic acid (PLA) to attain composite films of PLA/carbon-WC deposited coir pulp. The deposition of carbon-WC on coir pulp not only increased hydrophobicity of coir pulp but also improved compatibility between the filler and PLA. Even at the low filler content of 0.75 wt%, tensile strength and Young’s modulus of composite films of PLA/carbon-WC deposited coir pulp increased up to 45.73% and 22.79%, respectively compared with those of neat PLA film. Furthermore, the presence of carbon-WC deposited coir pulp in the PLA composite films could enhance the formation of crystalline structure of PLA. Accordingly, SPP is an interesting tool for surface modification of coir pulp in order to achieve surface-functionalized coir pulp for using as a filler in green composites.

Effects of electrode configurations, solution pH, TiO2 addition on hydrogen production by in-liquid discharge plasma

In-situ hydrogen production for mobile transportation has gradually become a research hotspot with the adjustment of energy structure. Especially hydrogen production from liquid materials can avoid the problems of storage and transportation. In this work, hydrogen produced by in-liquid discharge from ethanol/water mixtures was researched. The effects of electrode configurations, solution pH, commercial TiO2 addition on hydrogen production were specially discussed. The results show that the acid solution is conducive to increasing the percentage concentration of hydrogen, and discharge in the alkaline solution can increase the flow rate of hydrogen at high voltage. Meanwhile, the needle-12 needles configuration is more suitable for in-liquid pulsed discharge for hydrogen production that the energy efficiency is higher compared with other configurations. In-liquid discharge coupled with TiO2 addition can improve the effect of hydrogen production to a certain extent. With 4 mg/L TiO2 concentration, the flow rate and percentage concentration of hydrogen can increase about 30%, 2.6%, respectively.

Development of dispersive liquid using in-liquid plasma

Development of dispersive liquid using in-liquid plasma

Microwave plasma discharges for biomass pretreatment: Degradation of a sodium carboxymethyl cellulose model

Biogas production is an important component of an environmentally benign renewable energy strategy. However, the cost-effectiveness of biogas production from biomass is limited by the presence of polymeric structures, which are recalcitrant to digestion by bacteria. Therefore, pretreatments must often be applied prior to anaerobic fermentation to increase yields of biogas. Many physico-chemical pretreatments have a high energy demand and are generally costly. An alternative could be the ignition of a plasma directly in the biomass substrate. The reactive species that are generated by plasma–liquid interactions, such as hydroxyl radicals and hydrogen peroxides, could contribute significantly to the disintegration of cell walls and the breakage of poorly digestible polymers. With respect to economic, processing, and other potential benefits, a microwave instigated and sustained plasma was investigated. A microwave circuit transmitted 2-kW pulses into a recirculated sodium carboxymethyl cellulose solution, which mimicked the rheological properties of biomass. Each microwave pulse had a duration of 12.5 ms and caused the ignition of a discharge after a vapor bubble had formed. Microwaves were absorbed in the process with an efficiency of ∼97%. Slow-motion imaging showed the development of the discharge. The plasma discharges provoked a decrease in the viscosity, probably caused by the shortening of polymer chains of the cellulose derivative. The decrease in viscosity by itself could reduce processing costs and promotes bacterial activity in actual biomass. The results demonstrate the potential of microwave in-liquid plasma discharges for the pretreatment of biomass.

One-step Ammonia Synthesis by In-liquid Plasma under Ordinary Temperature and Pressure

One-step Ammonia Synthesis by In-liquid Plasma under Ordinary Temperature and Pressure

Quality improvement of deteriorated cutting fluid treated by atmospheric-pressure plasma jet and in-liquid plasma

Quality improvement of deteriorated cutting fluid treated by atmospheric-pressure plasma jet and in-liquid plasma

Simultaneous Synthesis of Diamond and Hydrogen

A relationship between diamond synthesis and hydrogen production in in-liquid plasma method have been investigated. Approximately 60 % energy can be recovered by collecting hydrogen gas made by ingredient solution decomposition. The relationship is trade-off. When higher energy is used to maintain the substrate temperature, the hydrogen production rate gets faster, but the diamond synthesis rate gets slower. To increase diamond synthesis rate, a method should be established which maintains the substrate temperature by lower energy and generates less hydrogen gas.

Fuel Production and Materials Synthesis by In-liquid Plasma

The in-liquid plasma process has been utilized to produce fuel gases from various liquids such as hydrocarbon and alcohol liquids, electrolytes, waste oil, biomass solutions, including glucose and cellulose, as well as to synthesize Zn, ZnO, WO3, Mg(OH)2 nanoparticles and diamonds. Using this technology, zero-emission hydrogen generation could become possible because it enables liquids to be directly broken down by plasma, making possible the decomposition of waste substances while producing useful materials. The application of the in-liquid plasma process for hydrogen production, decomposition of biomass, and synthesis of materials has already produced significant results. These highlight data will provide new information on “in-liquid plasma application.

Plasma in-Liquid Using Non-contact Electrodes: A Method of Pretreatment to Enhance the Enzymatic Hydrolysis of Biomass

Dielectric Barrier Discharge (DBD) can be used to produce a large volume of non-thermal plasma at atmospheric pressure. Such plasmas are sources of highly reactive species (radicals, ozone, atoms, ions and excited molecules). Due to its characteristics, the DBD plasma can be applied for the pretreatment of lignocellulosic materials, in order to extract lignin that prevents the access to remained fermentable sugars in the biomass. In this context, an alternative method for pretreatment of lignocellulosic material in an in-liquid DBD plasma reactor using non-contact electrodes, working with atmospheric air, has been proposed. After the pretreatment, the solids were washed and submitted to enzymatic hydrolysis with a commercial enzyme complex, at 10 FPU/g of pretreated biomass and 50 g/L solids concentration (dry basis), for 72 h. The release of fermentable sugars was measured, comparing the samples obtained with and without plasma treatment. The highest sugar release was achieved using the plasma-in-liquid pretreatment in a single step, with glucose and xylose yields of 51.3 and 38.5%, respectively, after enzymatic hydrolysis. Thus, an effective pretreatment was developed to be applied to biomass such as: corn cob, sugarcane bagasse, bamboo, eucalyptus, etc., in order to reduce the environmental impact and, at the same time, produce biofuels.

Formation of two kinds of carbon with different properties by acetone decomposition using in-liquid plasma method

Most waste solvent treatment methods involve combustion; however, such methods emit carbon dioxide and are also problematic relative to energy costs. As well as reducing carbon dioxide generate, in-liquid plasma has been used to generate valuable substances and hydrogen energy from the waste solvent. As a waste solve treatment model, decomposition of acetone using 27.12 MHz in-liquid plasma was performed at atmospheric pressure. The produced gases were H2, CO, CH4, C2H2, C2H4, C2H6, and CO2, where proportion of CO2 was less than 0.25%. Two types of carbons with different properties were obtained as byproducts during the acetone decomposition. These carbons analyzed using elemental analysis and Raman spectroscopy. The analysis results revealed that the crystallinity of the carbons different significantly. Undesirable organic matter, such as benzene, was also produced during acetone decomposition. The acetone decomposition efficiency at 407 W discharge power was 0.9 μmol J−1.

Effect of introducing a steam pipe to n-dodecane decomposition by in-liquid plasma for hydrogen production

A method has been developed to improve the hydrogen production efficiency (HPE) by in-liquid plasma n-dodecane decomposition. A thin steam pipe is placed over the plasma electrode to recover the thermal energy emitted from the plasma to its surroundings. The steam generated by this energy is supplied to the vaporized n-dodecane around the edge of the plasma to cause a steam reforming reaction (SRR). Water pyrolysis is suppressed by not supplying the steam directly to the plasma. A large amount of CO and a small amount of CO2 were detected in the produced gas. This indicates that a strong SRR has occurred. The HPE obtained by this method is 0.28 Nm3/kWh, which is two times greater than those obtained by previous methods, and similar to or greater than the yield of water electrolysis. This result is a major advance in the field of plasma heavy hydrocarbon decomposition aimed at hydrogen production. HPE is expected to be further improved by simply increasing the input power, due to synergy between the heat recovery effect of the steam pipe and the bubble stabilization effect. This indicates that this method has a high potential.

Mechanism of E. coli Inactivation by Direct-in-liquid Electrical Discharge Plasma in Low Conductivity Solutions

This work investigates and reveals the main mechanism(s) responsible for inactivation of E. coli by in-liquid pulsed electrical discharge plasma in low conductivity solutions. Experiments were designed and performed to explore the effects of plasma-emitted UV light, oxidative radicals, and electric field on E. coli inactivation curves, rate of DNA leakage and visual appearance of the treated microorganisms. Results showed that electric field had the main role in inactivation; scanning electron microscopy images revealed that both plasma and the isolated electric field result in extensive cell wall disruptions. While this damage in the case of plasma treatment was extensive and distributed randomly along the envelope, the electric field-induced damage resulted in disruption primarily at the poles of the bacterial rods. Subsequent experiments conducted with an oxidative radical scavenger suggested that plasma-generated radicals do not contribute directly to the inactivation but assist in cell wall deterioration and extension of the ruptures first generated by the electric field.

Facile synthesis of SnO2-graphene composites employing nonthermal plasma and SnO2 nanoparticles-dispersed ethanol

The tin oxide (SnO2)-graphene composite was synthesized by the in-liquid plasma method using SnO2 nanoparticles (average diameter ~30 nm) dispersed ethanol as a precursor without providing external heat. As observed from scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the SnO2 nanoparticles were distributed uniformly on flaky graphene sheets. The formation of SnO2 and high crystalline graphene was supported by the Raman analysis and x-ray diffraction (XRD) studies. A facile, low-cost method operating at atmospheric pressure based on the in-liquid plasma technology can be utilized to fabricate SnO2-graphene composite using minimum precursors for future applications such as gas sensing devices and fuel cells.

Single-Step, Low-Temperature Simultaneous Formations and in Situ Binding of Tin Oxide Nanoparticles to Graphene Nanosheets by In-Liquid Plasma for Potential Applications in Gas Sensing and Lithium-Ion Batteries

The in situ binding of tin oxide (SnO2) nanoparticles (SNp) and graphene nanosheets (GNs) that synthesized simultaneously in single-step atmospheric-pressure processing was achieved at a low temperature by employing in-liquid plasma in a solution of tin chloride (SnCl2·2H2O) in ethanol as the only precursor. Transmission electron microscopy, Raman analysis, and X-ray diffraction revealed the composite (SNp/GNs) synthesis with SNp of sizes 2−3 nm, which were distributed uniformly and attached to both sides of the GNs. The SNp/GNs composite synthesis was provided by the simple, low-cost, single-processing method of the in-liquid plasma for future gas-sensing and lithium-ion battery applications.

Synthesis of nano-carbon by in-liquid plasma method and its application to a support material of Pt catalyst for fuel cell

One of the applications of nano-carbon is a support material of platinum (Pt) catalyst for fuel cells. In this study, the nano-carbon was successfully synthesized by in-liquid plasma in ethanol. The synthesized nano-carbon was characterized by the transmission electron microscope and the Raman spectroscopy. Moreover, the nano-carbon was applied to a support material of Pt catalyst for a proton exchange membrane fuel cell. The formation of the Pt particles on the nano-carbon was also carried out using the in-liquid plasma. The formed Pt/nano-carbon worked as a catalyst of the fuel cell. The fuel cell, fabricated with the Pt/nano-carbon catalyst, generated the maximum output power of 580 mW.

High-speed synthesis of heavily boron-doped diamond films by in-liquid microwave plasma CVD

Here, we report the first synthesis of polycrystalline boron-doped diamond (BDD) by an In-liquid microwave plasma CVD (IL-MPCVD) process from a mixture of alcohols and boron trioxide (B2O3). We simultaneously achieved high growth rates (up to 287 μm/h) and high boron concentrations (up to 7 × 1021 cm−3). We examined the growth mechanism and show that water generated by dissolution of B2O3 in the alcohol is key to rapid growth of BDD. Even with the same C:H:O ratio, diamond growth rate and nucleation density drastically decreased by addition of water. Water has a strong etching effect, which shifts diamond to grow in carbon rich conditions. Finally, we evaluated the as-grown BDD film as a diamond electrode. Our IL-MPCVD-grown BDD showed electrochemical properties comparable to those of BDD grown by the conventional CVD process in terms of its potential window (3.2 V) and peak separation (85 mV) in 1 mM K3[Fe(CN)6]. Owing to the high growth rate, IL-MPCVD is an effective technique for synthesizing BDD.